This invention relates to a linear bearing, particularly a linear bearing that can be used in applications requiring high rigidity, such as guide posts of presses and molds.
A linear bearing that provides a mechanism for linear movement along a shaft consists of a guide shaft, an outer cylinder capable of moving in the axial direction relatively to the guide shaft outside the guide shaft, numerous rolling elements interposed between the guide shaft and the outer cylinder, and a cage provided between the guide shaft and the outer cylinder for retaining said numerous rolling elements disposed in the circumferential direction and in the axial direction. The rolling elements used include balls, rollers, needle rollers, etc.
In a linear bearing using balls as the rolling elements, since the outer surface of the guide shaft and the inner surface of the outer cylinder for having the balls interposed between them are formed as smooth cylindrical surfaces, the relative motion between the outer cylinder and the guide shaft around the axis is free, to provide an advantage that assembling is easy. However, since the contacts of the balls as the rolling elements with the inner surface of the outer cylinder and the outer surface of the guide shaft are point contacts, the rigidity is likely to be insufficient disadvantageously. The rigidity can be enhanced by a method of increasing the number of balls interposed between the outer cylinder and the guide shaft, but there is a limit in the number of interposed balls. So, there is also a limit in the rigidity that can be achieved.
On the other hand, in a linear bearing using rollers as the rolling elements, the inner surface of the outer cylinder and the outer surface of the guide shaft are formed to have flat and parallel rolling faces, and the rollers are interposed between these flat and parallel rolling faces. In this case, since the contacts of the rollers with the respective flat rolling faces are line contacts, the rigidity can be enhanced compared to the abovementioned linear bearing using balls as the rolling elements. However, forming the flat and parallel rolling faces on the inner surface of the outer cylinder and the outer surface of the guide shaft requires an advanced machining technique, to raise the production cost. Furthermore, in this case, the relative motion between the outer cylinder and the guide shaft around the axis is not free. So, when the guide shaft and the outer cylinder are assembled with the respective components of a mating apparatus, those components must be accurately positioned and complicatedly adjusted very inconveniently.
The object of this invention is to solve the above-mentioned problems of the prior art, by providing a linear bearing that has high rigidity, can be easily produced, can be kept low in production cost, and can be easily assembled with a mating apparatus.
To achieve the above object, this invention proposes, first of all, a linear bearing, that is composed of a guide shaft, an outer cylinder capable of moving relatively to the guide shaft in the axial direction outside the guide shaft, numerous rolling elements interposed between the guide shaft and the outer cylinder, and a cage provided between the guide shaft and the outer cylinder for retaining said numerous rolling elements disposed in the circumferential direction and in the axial direction, characterized in that each of the rolling elements is a roller having a convex circular arc surface of revolution formed on the cylindrical surface thereof, that the inner surface of the outer cylinder and the outer surface of the guide shaft are formed as cylindrical surfaces respectively, that the radius of the circle constituting the circular arc surface of revolution of each of the rollers is kept slightly smaller than the radius of the circle constituting the cylindrical surface of the outer cylinder, and that the pitch of the rollers disposed in the circular direction is smaller than twice the width of each roller.
In the linear bearing as the above subject matter of this invention, the circular arc surfaces of revolution fonned on the cylindrical surfaces of the rollers are kept in contact with the cylindrical inner surface of the outer cylinder and the cylindrical outer surface of the guide shaft, and since the circular arc surfaces of revolution formed on the cylindrical surfaces of the rollers are adapted to the inner cylindrical surface of the outer cylinder, the contacts between the rollers and the outer cylinder can be considered to be substantially line contacts. So, the rigidity can be kept high. Furthermore, since the inner surface of the outer cylinder and the outer surface of the guide shaft can be formed as cylindrical surfaces, the forming work is easy and can keep the production cost low.
Moreover, because of the constitution as described above, in which the inner surface of the outer cylinder and the outer surface of the guide shaft are cylindrical surfaces and in which the circular arc surfaces of revolution of the rollers contact the outer cylinder and the guide shaft, the outer cylinder and the guide shaft can rotate relatively to each other around the axis, that is, the relative motion around the axis is free. So, the linear bearing can be easily assembled with a mating apparatus.
Furthermore, since the pitch of rollers disposed in the circular direction is smaller than twice the width of each roller, more rollers can be disposed along the circumference with the same diameter. So, compared with the conventional constitution in which the pitch of the rollers disposed in the circumferential direction is larger than twice the width of each roller, higher rigidity can be obtained if the diameter of the circumference along which the rollers are disposed is the same, or the diameter of the circumference can be made smaller, that is, the outer cylinder can be downsized, if it is intended to achieve equivalent rigidity.
This invention also proposes a linear bearing, that is composed of a guide shaft, an outer cylinder capable of moving in the axial direction relatively to the guide shaft outside the guide shaft, numerous rolling elements interposed between the guide shaft and the outer cylinder, and a cage provided between the guide shaft and the outer cylinder for retaining said numerous rolling elements disposed in the circumferential direction and in the axial direction, characterized in that each of the rolling elements is a roller having a convex circular arc surface of revolution formed on the cylindrical surface thereof, that the inner surface of the outer cylinder is formed as a cylindrical surface, that the outer surface of the guide shaft is provided with axially extending guide grooves, each having a concave cylindrical surface, corresponding to the respective rows of the rollers disposed in the axial direction, that the radius of the circle constituting the circular arc surface of revolution of each of the rollers is kept slightly smaller than the radius of the circle constituting the cylindrical surface of the outer cylinder and the radius of the circle constituting the concave cylindrical surface of each of the grooves formed in the guide shaft, and that the pitch of the rollers disposed in the circumferential direction is kept smaller than twice the width of each roller.
In the linear bearing as this subject matter of this invention, since the circular arc surfaces of revolution formed on the cylindrical surfaces of the rollers contact the inner cylindrical surface of the outer cylinder and the concave cylindrical surfaces of the guide grooves of the guide shaft, the contacts of the circular arc surfaces of revolution of the rollers with the inner surface of the outer cylinder and the guide grooves of the guide shaft can be considered to be substantially line contacts. So, compared with the previous subject matter, this subject matter allows higher rigidity to be achieved.
In this subject matter of the present invention, as described above, in order to further enhance the rigidity, the guide shaft has guide grooves formed, each having a concave cylindrical surface. However, since it is only required that the guide grooves are formed on the outer surface of the guide shaft, the pitch accuracy of the guide grooves around the guide shaft is not so important, and the forming work is easy. In addition, the inner surface of the outer cylinder is a cylindrical surface. So, since the outer cylinder and the guide shaft can rotate relatively to each other around the axis, that is, the relative motion around the axis is free, the linear bearing can be easily assembled with a mating apparatus.
Also in this subject matter of the invention, as in the previous subject matter, the pitch of the rollers disposed in the circumferential direction is kept smaller than twice the width of each roller. Therefore, more rollers can be disposed along the circumference with the same diameter. So, compared with the conventional constitution in which the pitch of the rollers disposed in the circumferential direction is larger than twice the width of each roller, higher rigidity can be achieved if the diameter of the circumference along which the rollers are disposed is the same, or the diameter of the circumference can be made smaller, that is, the outer cylinder can be downsized, if it is intended to achieve equivalent rigidity.
In the subject matters described above, this invention also proposes a constitution in which each of the rollers has a width smaller than its diameter.
In this subject matter of the invention, since further more rollers can be disposed along the circumference with the same diameter, further higher rigidity can be achieved if the diameter of the circumference along which the rollers are disposed is the same, or the diameter of the circumference can be made further smaller, that is, the outer cylinder can be further downsized, if it is intended to achieve equivalent rigidity.
In the invention described above, it is suitable that the radius of the circle constituting the circular arc surface of revolution of each roller is set at 93% to 96% of the radius of the circle constituting the cylindrical surface of the outer cylinder.
Furthermore, in the invention described above, it is suitable that the radius of the circle constituting the concave cylindrical surface of each guide groove is set at 1.04 to 1.08 times the radius of the circle constituting the circular arc surface of revolution of each roller,
Moreover, in the invention described above, it is suitable that the radius of the circle constituting the concave cylindrical surface of each of the guide grooves of the guide shaft is set to be equal to the radius of the circle constituting the cylindrical surface of the outer cylinder, but they can also be different, as the case may be.